Asbestos treatment with metal molybdates

ABSTRACT

A method of treating asbestos comprising depositing on at least a portion of the asbestos a material consisting essentially of at least one metal molybdate.

BACKGROUND OF THE INVENTION

This invention relates to asbestos. More in particular, the presentinvention relates to a method of treating asbestos.

"Asbestos" is a general term applied to a group of naturally occurringfibrous silicate minerals that are commercially important because oftheir fibrous characteristics. Four principal types of asbestos mineralsgenerally enter world commerce. These are chrysotile, crocidolite,amosite and anthophyllite. Of these, chrysotile is perhaps that mostimportant, accounting for about 95 percent of the world's asbestosproduction.

Chemically, chrysotile asbestos is the fibrous form of the mineralserpentine, a hydrated magnesium silicate having the general formula Mg₃Si₂ O₃ (OH)₄. Structurally the chrysotile asbestos is believed toconsist of rolled up sheets formed from two layers. The first layer is acontinuous network of silica (SiO₂) tetrahedra. This layer isinterlocked through common oxygen atoms with a second layer of magnesiumhydroxide (Mg(OH₂)) octahedra. The walls of the asbestos fibers arecomposed of a number of such individual sheets contorted into scrollswith the magnesium hydroxide layer on the outside. Consequently, one ofthe dominant chemical features of chrysotile asbestos is its alkalinesurface characteristics.

The surface modification of asbestine minerals, such as chrysotile, hasattracted a good deal of attention from research workers during recentyears. A large number of surface treatment methods have been proposedand evaluated for the purpose of modifying certain predeterminedproperties of the asbestos fibers. These procedures include: coating thesurface of asbestos fibers with a phosphate, polyphosphate, orcorresponding acid to improve the filtration characteristic of thefibers (U.S. Pat. Nos. 3,535,150, 3,957,571); treating asbestos fiberswith magnesium carbonate or an oxide of a polyvalent metal to enhancethe tensile strength of the fibers (U.S. Pat. Nos. 1,982,542; 2,451,805;2,460,734); coating an asbestos fabric with an insoluble inorganic oxideto render the fabric flame resistant and water repellent (U.S. Pat. No.2,406,779); mixing a detergent organic surface-active agent with fibrousasbestos agglomerates to disperse the asbestos fibers (U.S. Pat. No.2,626,213); and distributing small amounts of polymeric particles or awater-soluble macromolecular organic substance throughout an asbestosproduct to reduce dust emitted by the asbestos during handling and use(U.S. Pat. Nos. 3,660,148; 3,967,043).

An area of concern to the producers and users of asbestine material hasbeen the potential health problems allegedly associated with asbestosexposure. It has been reported by the National Safety Council thatpersons who inhale large amounts of asbestos dust can develop disablingor fatal pulmonary and pleural fibrosis (asbestosis) and several typesof malignancy of the respiratory tract ("Asbestos", National SafetyCouncil Newsletter, R & D Section, June 1974). There is also speculationthat asbestos may cause various forms of carcinogenesis, particularlycarcinoma of the lung, pleura and peritoneum (R. F. Holt, "Asbestosis",Nature, 253, 85 (1975)). Since the pathogenicity of asbestos minerals isapparently unmatched by any other silicate, there has been much interestin developing a method of passivating asbestos to reduce any potentialfibrogenic and carcinogenic effects on those exposed to it withoutadequate precaution.

Existing methodology for studying the in vivo fibrogenic effects ofasbestos involves direct inhalation or intratracheal administration ofasbestos fibers to animals. Subsequently, the experimentally treatedanimals are examined, usually months later, for pathological andhistochemical evidence of fibrosis. Since the incubation period forasbestos-induced diseases is reported to be unusually long, experimentsof this type are complicated, expensive and time consuming.

However, recent work done by R. R. Hefner, Jr. and P. J. Gehring(American Industrial Hygiene Association Journal, 36, 734-740 (1975))shows that a relationship exists between the in vivo fibrogenicity ofasbestos and its in vitro hemolytic activity. Hemolytic activity, orhemolysis, is a measure of induced blood cell rupture when fibers areagitated with a suspension of blood erythrocytes. Numerous other authorshave also made similar in vitro evaluations of a number of particulates.

The in vitro hemolytic model provides a rapid, relatively inexpensivetest which reliably assesses the fibrogenic potential of asbestos.Consequently, the hemolytic model has been employed in the presentinvention to test the effectiveness of certain asbestos treatingprocedures found to be potentially useful in alleviating some of thehealth problems reportedly associated with asbestos fibers.

Various materials have been examined which interact with the surface ofasbestos fibers and reduce its hemolytic activity. Such materialincludes disodium ethylenediamine tetraacetic acid (EDTA), simplephosphates, disodium versenate, polyvinylpyridine N-oxide and aluminum(G. Macnab and J. S. Harington, Nature 214, 522-3 (1967), and certainacidic polymers (R. J. Schnitzer and F. L. Pundsack, EnvironmentalResearch 3, 1-14 (1970). In addition, West German Pat. No. 1,642,022discloses that asbestos coated with polyvinylpyridine N-oxide minimizesthe risk of asbestosis.

Some of these known materials, such as EDTA, are solubilized in bodyfluids and do not reduce the long term hemolytic activity of theasbestos. There is therefore a need to determine materials which willadhere to the asbestos and reduce its hemolytic activity. Suchpassivating materials should not adversely affect the useful commercialproperties of the asbestos.

SUMMARY OF THE INVENTION

The present invention is a method for treating asbestos comprisingdepositing on at least a portion of the asbestos a material consistingessentially of at least one metal molybdate.

Using a hemolysis test described herein, as an in vitro screening testto assess the effectiveness of the metal molybdate treatment, it hasbeen surprisingly found that asbestos fibers with at least one metalmolybdate deposted thereon have reduced hemolytic activity in comparisonwith untreated asbestos fibers.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the present invention, asbestos is treated to depositat least one metal molybdate on at least a portion of the asbestos.

A number of suitable deposition techniques can be employed to treat theasbestos. For example, the asbestos can initially be contacted with asolution of an ionizable salt of at least one first metal to deposit atleast a portion of the ionizable salt on the asbestos. The ionizablesalt-treated asbestos is subsequently contacted with a solution of amolybdate salt of at least one second metal to form a molybdate of atleast one first metal on at least a portion of the surface of theasbestos.

Alternatively, the asbestos can initially be contacted with a solutionof molybdate salt of at least one second metal to deposit at least aportion of the molybdate salt of the second metal on the asbestos. If itis desirable to have another metal molybdate, in addition to, or otherthan, the second metal molybdate deposited on the asbestos, themolybdate salt-treated asbestos can optionally be contacted with asolution of an ionizable salt of at least one first metal, to form amolybdate of at least one first metal on at least a portion of theasbestos.

In another embodiment, the metal molybdates can be deposited on theasbestos by directly contacting the surface of the asbestos with asuspension of at least one first metal molybdate in a liquid medium,such as water. One suitable technique involved suspending a particulatefirst metal molybdate in water, spraying the suspension onto the surfaceof the asbestos, and removing the water by drying. First metalmolybdates which can be suitably applied in this manner include thosethat are insoluble in the suspending medium.

For the purpose of this specification, the following definitions areadopted. The first series of transition metals begins with elementnumber 21, scandium, and continues through element number 29, copper.The second series of transition metal begins with yttrium, number 39,and ends with silver 47. The group II B metals are zinc, cadmium, andmercury. The group III metals are aluminum, gallium, indium, andthallium. The group IV metals are germanium, tin, and lead. Theoxidation state (valence) of metals which commonly exhibit more than onevalence is indicated by a Roman numeral in perentheses following themetal to which it refers. The terms ionizable salt and molybdate saltrefer to both the anhydrous and hydrated forms of the salts.

The methods of treating the asbestos include depositing an ionizablesalt of at least one suitable first metal on at least a portion of theasbestos. In this context an ionizable salt is defined as a salt whichdissociates spontaneously into cations and anions when dissolved in asuitable polar solvent, such as water, formamide, acetamide, ethanol,1-propanol, dimetyl sulfoxide, methanol, mixtures thereof, and the like.The preferred solvent is water.

Any metal cation which is capable of forming a molybdate salt can beused as a first metal. Preferably, the first metal cation is selectedfrom the alkali metals, alkaline earth metals, first series transitionmetals, second series transition metals, group II B metals, group IIImetals, and group IV metals.

More preferably, the alkali metal is sodium; the alkaline earth metal isselected from the group consisting of magnesium, calcium, and barium;the first series transition metal is selected from the group consistingof titanium (III), titanium (IV), chromium, manganese, iron (II), iron(III), cobalt, and nickel; the second series transition metal isselected from the group consisting of zirconium and silver; the groupIII metal is aluminum; the group IV metal is selected from the groupconsisting of tin (II), tin (IV), and lead; and the group II B metal isselected from the group consisting of zinc and cadmium. Most preferably,the first metal cation is tin (II), tin (IV), or a mixture thereof.

Suitable second metal cations are those which form soluble molybdatesalts, preferably, water soluble molybdate salts. The preferred secondmetal cations are the alkali metals, and more preferably, sodium,potassium, or a mixture thereof.

Any ionizable salt which will ionize in solution to produce a cation ofat least one of the above first metal cations can be used in the presentprocess. However, the preferred ionizable salt is a chloride, sulfate,nitrate, or a mixture thereof of at least one of the first metals. Morepreferably, the ionizable salt is a water soluble chloride salt of atleast one of the first metals. Furthermore, the ionizable salt cancontain more than one type of cation and one type of anion. For example,a mixture of chloride salts of two first metals, or a mixture of thechloride and sulfate salts of the same first metal is suitable.

The concentration of the solution of the ionizable salt employed in thepresent process is sufficient to form a deposit of the ionizable salt onthe asbestos. Preferably, the concentration of the solution of theionizable salt is from about 1 percent by weight of the salt to aboutthe concentration corresponding to a saturated solution of theparticular first metal salt. For example, when nickel chloridehexahydrate is the ionizable salt, the concentration of the salt in anaqueous salt solution at 20° C. and 1 atmosphere pressure is from about1 to about 72 percent by weight. More preferably, the concentration ofthe solution of the ionizable salt is from about 5 to about 10 percentby weight of the salt.

A number of suitable techniques are known for initially applying theionizable salt solution compounds to the asbestos. These techniquesinclude spraying the ionizable salt solution onto the asbestos orsoaking the asbestos in the ionizable salt solution. The preferredmethod of contacting the asbestos with the ionizable salt solution is byslurrying the asbestos in the ionizable salt solution for a sufficienttime to allow the surface of the asbestos to be contacted and wetted bythe solution.

Advantageously, the mixture of asbestos and the ionizable salt solutioncan then be agitated at room temperature for a sufficient time to allowthe ionizable salt solution to contact at least a portion, andpreferably substantially all of the asbestos surfaces. The agitation ofthe mixture is accomplished by use of agitation means well-known in theart. These include mechanical, air, hydraulic or magnetic means forinducing agitation.

Following agitation, the asbestos suspended in the ionizable saltsolution can be separated from the filtrate (ionizable salt solution) byany suitable solid-liquid separation technique such as vacuumfiltration. The ionizable salt-treated asbestos can then be contactedwith a solution, preferably an aqueous solution, of a molybdate salt ofat least one of the second metals. The techniques for applying theionizable salt solution discussed above can be used to contact theionizable salt-treated asbestos with the molybdate salt solution.However, it is preferred to slurry the ionizable salt-treated asbestoswith the molybdate salt solution. The ionizable salt-treated asbestos ismaintained in contact with the molybdate salt solution for a sufficienttime to allow at least a portion, and preferably substantially all themolybdate salt solution to contact the ionizable salt-treated asbestosand react with the ionizable salt thereon to form a metal molybdatecompound wherein the cation of said compound is originally the cation ofthe first metal associated with the ionizable salt.

The molybdate salt solution has a concentration sufficient to form adeposit of the molybdate salt on the asbestos. Preferably, theconcentration of the molybdate salt solution is from about 1 percent byweight to about the concentration corresponding to a saturated solutionof the molybdate of the second metal. For example, when sodium molybdate(Na₂ MoO₄.2H₂ O) is employed, the concentration of the salt in anaqueous solution at 20° C., 1 atmosphere pressure, is from about 1 toabout 36 percent by weight of the sodium molybdate. Preferably, themolybdate salt solution has a concentration of from about 1 to about 10percent by weight of the second metal molybdate.

The asbestos-molybdate salt solution slurry is preferably agitated atabout room temperature for a sufficient time to insure contact betweenthe asbestos and the molybdate salt solution.

Following agitation, the asbestos is separated from the filtrate by anysuitable solid-liquid separation technique, such as vacuum filtration.Preferably the filtered asbestos is subsequently washed with a suitablesolvent, such as deionized water, to remove any non-adherent molybdatecompound. The asbestos can then be dried by any suitable techniques,such as air drying, heating, vacuum and the like.

The asbestos treated by the present method is characterized as being afibrous asbestos material consisting essentially of asbestos fibers witha coating of at least one first or second metal molybdate deposited onat least a portion of the asbestos fibers. Preferably, the asbestosmaterial consists of asbestos fibers coated with substantially only ametal molybdate. Any metal cation capable of forming a molybdate salt onthe asbestos can be used. Examples of preferred first and second metalshave been described above.

The asbestos treated by the present invention can include chrysotile,crocidolite, amosite, or anthophyllite asbestos. Chrysotile, being themost abundant type of asbestos, is the preferred material for treatmentby the present process. The physical form of asbestos treated includesfibrous mineral bundles of fine crystalline fibers, or individualfibers. Preferably the asbestos is in the form of bundles of crystallinefibers. Generally, the individual fibers of the bundle have a fiberlength of at least about 0.5 micron, and a diameter of at least about0.01 micron. However, other fiber lengths and diameters can be employed.

The exact mechanism by which the deposited metal molybdate forms anadherent coating on the asbestos is not completely understood. It isbelieved that the coating is due to the alkaline outer surface of theasbestos fiber. The individual fibers are composed of a network ofmagnesium hydroxide tetrahedra. The outermost portion of the tetrahedracontains hydroxyl groups. There is some evidence that hydroxyl hydrogensare being displaced by the metal cation, to form a bond between themetal molybdate and the asbestos. Since each asbestos fiber is composedof a number of individual sheets having outer hydroxyl groups, andbecause these sheets are contorted into concentric scrolls, thedeposition of the metal molybdate may occur on more than just theoutermost exposed surface of the asbestos fiber. Some of the metalmolybdate may impregnate the interior scrolls of the fiber and depositon the interior hydroxyl surface present.

Any amount of metal molybdate is beneficial to reduce hemolysis.However, the metal molybdate that is deposited on the asbestos ispreferably present in an amount of from about 0.05 to about 5.0 percentby weight based on the weight of the asbestos. The metal molybdatedeposited on the exposed asbestos surface is from about 0.5 to about 250angstroms thick. Preferably, the molybdate surface coating is from about2 to about 50 angstroms thick. As recognized by those skilled in theart, the thickness of the surface coating can vary depending on thenature of the asbestos, its intended end use, and economics.

The following examples further illustrate the present process.

EXAMPLES

A regular grade of Carey 7RF-9 Canadian chrysotile asbestos was used inall of the following examples. The asbestos had a mean fiber length ofabout 30 microns, and contained about 10-15 percent by weight ofimpurities. The impurities present were characterized by X-raydiffraction and were found to be about 5 percent by weight Fe₃ O₄, about5-10 percent by weight Mg(OH)₂ and fractional weight percents (less than1 percent by weight) of each of minor impurities generally associatedwith commercially pure chrysotile asbestos, such as aluminum, chromium,cobalt, scandium and the like.

EXAMPLE 1

Fifteen grams (g) of the asbestos were placed in a 500 milliliters (ml)flask at 20° C. and 1 atmosphere pressure. To this was added 300 ml ofan aqueous SnCl₂.2H₂ O solution containing 10 percent by weightSnCl₂.2H₂ O.

The resultant slurry was agitated by use of a magnetic stirring bar toinsure uniform dispersion of the SnCl₂.2H₂ O throughout the asbestosfibers. Agitation of the slurry in this manner was maintained for 60minutes at room temperature. The slurry was then filtered by vacuumfiltration using Whatman #1 filter paper and a porcelain Buchner funnel.

While still moist, the asbestos fibers were reslurried with 100 ml of anaqueous solution containing 10 percent by weight Na₂ MoO₄.2H₂ O togetherwith 500 ml of deionized water in an 800 ml beaker. The resultant slurrywas agitated by magnetic stirring for 15 minutes. The slurry wasfiltered by vacuum filtration using a Whatman #1 filter paper and aporcelain Buchner funnel. The filtered asbestos fibers were washed with500 ml of deionized water to remove any undeposited salts and allowed toair dry at room temperature for from 12 to 15 hours.

The chrysotile surface coating was characterized by X-ray diffractionand atomic absorption spectroscopy. A coating of tin (II) molybdate wasshown to be distributed along the surface of the asbestos fibers. Bothelectron emission spectroscopy and atomic absorption spectroscopy wereused to determine the amount of molybdate coating on the fibers. Theresults verified microscopy data in that about 2 angstroms of the tin(II) molybdate were coated on the fibers. High magnificationtransmission electron microscopy indicated no significant morphologicaldifferences between uncoated and coated fibers.

Since chrysotile asbestos is widely used for high temperatureinsulation, the thermal stability of the coated asbestos wasinvestigated. The differential thermal analysis of coated and uncoatedasbestos indicated that there was no appreciable difference in thermalstability due to the coating.

Hemolysis tests of the coated asbestos fibers were conducted in thefollowing manner: Whole rat blood was suspended in 200-300 ml ofISOTON®, an isotonic blood cell diluent, without an anticoagulant. Thewhole blood suspension was centrifuged and the red cells were collectedand washed in 200-300 ml volume of the pure isotonic diluent. Thewashing removed plasma which is known to inhibit blood hemolysis fromthe whole blood suspension. After subsequent centrifugation of thewashed cell suspension, a final blood suspension was prepared. Thissuspension was a 2 percent, by volume, concentration of centrifuged redblood cells in the isotonic diluent.

About 250 milligrams (mg) asbestos fibers were placed in tissue cultureflasks and a 25 ml volume of the 2 percent blood suspension was added toeach flask. The resultant mixture was agitated by mechanical means andplaced in a constant temperature (98.6±0.5° F.) water bath. The flaskswere incubated for 30 minutes in a mechanical shaking incubator at aslow, constant rate of 50 cycles per minute. Control blood suspensionswere incubated using the same procedure. Spontaneous hemolysis wasdetermined by incubating the 2 percent blood sususpension a small amount(less than one mg) of saponin powder (a known hemolytic agent).

The culture flasks were removed from the incubator after 30 minutes andthe contents of each flask were centrifuged. A 3 ml volume of theresultant supernatant liquid was withdrawn and diluted with deionizedwater to a volume of 100 ml. The absorbance of the diluted samples wasmeasured at 415 nanometer (nm) using a double-beam spectrophotometer.The diluted spontaneous hemolysis liquid was used as the referencesolution in all absorbance measurements. Percent hemolysis was definedas ##EQU1## where A_(H) was the absorbance of a sample with asbestosfibers and A₁₀₀ was the absorbance of the 100% hemolyzed sample.

The dramatic reduction of hemolytic activity induced by the depositedtin (II) molybdate is shown in Table I.

EXAMPLE 2

Twenty grams (g) of asbestos fibers were placed in an 800 ml beaker at20° C. and 1 atmosphere pressure. To this was added 400 ml of an Na₂MoO₄.2H₂ O solution containing 10 percent by weight Na₂ MoO₄.2H₂ O.

The resultant slurry was agitated by use of a magnetic stirring bar toinsure uniform dispersion of the Na₂ WO₄.2H₂ O throughout the asbestosfibers. Agitation of the slurry in this manner was maintained for about60 minutes at room temperature. The slurry was then filtered by vacuumfiltration using Whatman #1 filter paper and a porcelain Buchner funnel.

While still moist, the asbestos fibers were reslurried with 100 ml of anaqueous solution containing 10 percent by weight SnCl₄.5H₂ O, togetherwith 500 ml of deionized water in an 800 ml beaker. The resultant slurrywas further treated and tested for hemolysis as described in Example 1.

EXAMPLES 3-20

Examples 3-20 were prepared in substantially the same manner asdescribed in Example 1, except that salts of different metals were usedin the initial contacting step. The reduction of hemolytic activityinduced by the deposited metal moybdates is shown in Table I.

COMPARATIVE EXAMPLE A

Uncoated chrysotile asbestos was tested for hemolytic activity by themethod described in Example 1. The results are shown in Table I.

                  Table I                                                         ______________________________________                                        Hemolysis Induced by Molybdate Coating                                        on Chrysotile Asbestos                                                        Example       Coating    % Hemolysis                                          ______________________________________                                        1             SnMoO.sub.4                                                                              2                                                    2             FeMoO.sub.4                                                                              4                                                    3             Sn(MoO.sub.4).sub.2                                                                      8                                                    4             Ag.sub.2 MoO.sub.4                                                                       15                                                   5             BaMoO.sub.4                                                                              17                                                   6             Fe.sub.2 (MoO.sub.4).sub.3                                                               18                                                   7             CaMoO.sub.4                                                                              22                                                   8             Cr.sub.2 (MoO.sub.4).sub.3                                                               22                                                   9             PbMoO.sub.4                                                                              23                                                   10            CdMoO.sub.4                                                                              29                                                   11            CoMoO.sub.4                                                                              32                                                   12            MnMoO.sub.4                                                                              33                                                   13            Zr(MoO.sub.4).sub.2                                                                      33                                                   14            MgMoO.sub.4                                                                              45                                                   15            ZnMoO.sub.4                                                                              52                                                   16            Al.sub.2 (MoO.sub.4).sub.3                                                               55                                                   17            Na.sub.2 MoO.sub.4                                                                       57                                                   18            Ti(MoO.sub.4).sub.2                                                                      59                                                   19            Ti.sub.2 (MoO.sub.4).sub.3                                                               59                                                   20            NiMoO.sub.4                                                                              65                                                   A (Compara-   None       70                                                   tive)                                                                         ______________________________________                                    

The durability of the coatings of Examples 1, 2, 3, 4, and A wasdetermined by a series of attrition tests. The first-stage testsconsisted of washing the coated asbestos fibers sequentially with (1)water, (2) an aqueous solution of 0.1 normal (N) HCl, (3) an aqueoussolution of 0.1 N NaOH, and (4) acetone. Treated fibers were also testedfor durability by heat treatment for 3 hours at 150° C. and by grindingin a mechanical blender. After each of the six tests, the coated fiberswere reevaluated using the hemolysis test. The results of first-stageattrition test are outlined in Table II. The durability of a coating ina test was indicated by the difference in the hemolysis value before andafter attrition. An increase in the percent hemolysis, indicated thatthe coating was being removed by that test.

When the uncoated chrysotile was heated to 150° C. for three hours thehemolytic activity of the fibers was reduced from 70 percent to 12percent as shown in Table II. The reduction in hemolytic activity of theuncoated asbestos as a function of temperature and time was studied. Theresults indicated that no passivation of the fibers occurred throughheat treatment; instead, reversible dehydration of the fibers wasobserved.

                                      TABLE II                                    __________________________________________________________________________    First-Stage Attrition Tests with Coated Chrysotile Asbestos                              % Hemolysis                                                                       H.sub.2 O                                                                         0.1 N HC1                                                                           0.1 N NaOH                                                                           Acetone                                                                            Heated to                                Example                                                                            Coating                                                                             Initial                                                                           Wash                                                                              Wash  Wash   Wash 150° C./3 Hr                                                                  Ground                            __________________________________________________________________________         SnMoO.sub.4                                                                         2   2   2     5      1    0      1                                 2    FeMoO.sub.4                                                                         4   0   3     41     9    3      4                                 3    Sn(MoO.sub.4).sub.2                                                                 8   4   4     4      1    2      3                                 4    Ag.sub.2 MoO.sub.4                                                                  15  23  15    26     25   21     13                                A    None  70  77  40    75     78   12     78                                __________________________________________________________________________

Coatings which continued to show low hemolytic activity after subjectionto first-stage attrition test were tested in second-stage attritiontests. These tests included slurrying the coated fibers in deionizedwater for a period of up to 3 months and continuously washing the fiberswith water for up to 1 month. The hemolytic activity of the fibers wasmeasured periodically and the results are shown in Table III.

                  TABLE III                                                       ______________________________________                                        Second-Stage Attrition Test with Coated Chrysotile Asbestos                                                  Time  %                                        Ex.  Coating   Attrition Test  weeks Hemolysis                                ______________________________________                                        1    SnMoO.sub.4                                                                             Continuous Water Wash                                                                         0     2                                                       (95° C.) 2     3                                                                       4     40                                                      Water Slurry (25° C.)                                                                  0     2                                                                       4     0                                                                       8     3                                                                       12    3                                        2    Sn(MoO.sub.4).sub.2                                                                     Continuous Water Wash                                                                         0     8                                                       (95° C.) 2     12                                                                      4     16                                                      Water Slurry (25° C.)                                                                  0     8                                                                       4     7                                                                       8     9                                                                       12 4                                           ______________________________________                                    

The results presented in Tables I-III clearly indicate the significantreduction in hemolysis achieved by the present process. Untreatedasbestos ruptured about 70% of the available red cells in a bloodsuspension while the various molybdate coated fibers induced from 2 to65% hemolysis. Furthermore, the coatings on the chrysotile asbestos havebeen demonstrated to be extremely durable when subject to a rigorousseries of chemical and physical tests.

What is claimed is:
 1. A method of treating asbestos to reduce itshemolytic activity comprising depositing on at least a portion of theasbestos a material consisting essentially of at least onehemolysis-reducing metal molybdate in an amount of 0.5 to 5.0 percent byweight, based on the weight of the asbestos.
 2. The method of claim 1wherein the metal is selected from the group consisting of alkalimetals, alkaline earth metals, first series transition metals, secondseries transition metals, group II B metals, group III metals, and groupIV metals.
 3. The method of claim 2 wherein the alkali metal is sodium.4. The method of claim 2 wherein the alkaline earth metal is selectedfrom the group consisting of magnesium, calcium, and barium.
 5. Themethod of claim 2 wherein the first series transition metal is selectedfrom the group consisting of titanium (III), titanium (IV), chromium,manganese, iron (II), iron (III), cobalt, and nickel.
 6. The method ofclaim 2 wherein the second series transition metal is selected from thegroup consisting of zirconium and silver.
 7. The method of claim 2wherein the group III metal is aluminum.
 8. The method of claim 2wherein the group IV metal is selected from the group consisting of tin(II), tin (IV), and lead.
 9. The method of claim 2 wherein the group IIB metal is selected from the group consisting of zinc and cadmium.
 10. Amethod of treating asbestos to reduce its hemolytic activitycomprising:(a) contacting the asbestos with a solution of an ionizablesalt of at least one first metal to deposit at least a portion of theionizable salt on the asbestos; (b) contacting the asbestos with asolution of a molybdate salt of at least one second metal to form amolybdate of at least one first metal on at least a portion of thesurface of the asbestos.
 11. A method of treating asbestos to reduce itshemolytic activity comprising depositing on at least a portion of theasbestos a material consisting essentially at a hemolysis-reducing tin(II) molybdate.
 12. A method of treating asbestos to reduce itshemolytic activity comprising depositing on at least a portion of theasbestos a material consisting essentially of a hemolysis-reducing tin(IV) molybdate.
 13. The method of claim 10 wherein the second metal isan alkali metal.
 14. The method of claim 13 wherein the alkali metal isselected from the group consisting of sodium and potassium.
 15. Themethod of claim 10 wherein the first metal is selected from the groupconsisting of alkali metals, alkaline earth metals, first seriestransition metals, second series transition metals, group II B metals,group III metals, and group IV metals.
 16. The method of claim 10wherein the solution of the ionizable salt has a salt concentration offrom about 1 percent by weight to about a concentration corresponding tosaturated solution of the salt.
 17. The method of claim 10 wherein thesolution of the ionizable salt has a salt concentration of from about 5percent by weight to about 10 percent by weight of the salt.
 18. Themethod of claim 10 wherein the ionizable salt includes at least onemember selected from the group consisting of a chloride, a sulfate, anda nitrate.
 19. The method of claim 10 wherein the ionizable salt is achloride.
 20. The method of claim 10 wherein the solution of themolybdate salt has a concentration of from about 1 percent by weight toabout the concentration corresponding to a saturated solution of themolybdate of the second metal.
 21. The method of claim 10 wherein thesolution of the molybdate salt has a concentration of from about 1percent by weight to about 10 percent by weight of the molybdate of thesecond metal.
 22. The method of claim 10 wherein the solution of theionizable salt is an aqueous solution.
 23. The method of claim 10wherein the solution of the molybdate salt is an aqueous solution. 24.The method of claim 1 wherein the depositing step comprises spraying atleast a portion of the asbestos with at least one metal molybdatesuspended in a liquid medium.
 25. The method of claim 24 wherein themedium is water.
 26. The method of claim 1 wherein the depositing stepcomprises:(a) contacting the asbestos with a solution of a molybdatesalt of at least one second metal to deposit at least a portion of themolybdate salt on the asbestos; and optionally (b) contacting theasbestos from step (a) with a solution of an ionizable salt of at leastone first metal to form a molybdate of at least one first metal on atleast a portion of the surface of the asbestos.
 27. A method fortreating asbestos comprising:(a) slurrying the asbestos with asufficient amount of an aqueous solution of an ionizable salt of atleast one first metal selected from the group consisting of alkalimetals, alkaline earth metals, first series transition metals, secondseries transition metals, group II B metals, group III metals, and groupIV metals, to deposit at least a portion of the ionizable salt of atleast one first metal on at least a portion of the asbestos; (b)slurrying the asbestos from step (a) with an aqueous solution of amolybdate salt of at least one alkali metal to form about 0.05 to 5.0percent by weight, based on the asbestos a molybdate salt of at leastone first metal on at least that portion of the asbestos wherein theionizable salt of the first metal was deposited.
 28. The method of claim27 including agitating the asbestos and the aqueous solution of theionizable salt of the first metal for a sufficient time to allow theionizable salt to contact at least a portion of the asbestos.
 29. Afibrous asbestos material consisting essentially of asbestos fibershaving deposited thereon at least one hemolysis-reducing metal molybdateabout 0.05 to 5.0 percent by weight, based on the asbestos.
 30. Thematerial of claim 29 wherein the metal is selected from the groupconsisting of alkali metals, alkaline earth metals, first seriestransition metals, second series transition metals, group II B metals,group III metals, and group IV metals.
 31. The material of claim 30wherein the alkali metal is sodium.
 32. The material of claim 30 whereinthe alkaline earth metal is selected from the group consisting ofmagnesium, calcium, and barium.
 33. The material of claim 30 wherein thefirst series transition metal is selected from the group consisting oftitanium (III), titanium (IV), chromium, manganese, iron (II), iron(III) cobalt, and nickel.
 34. The material of claim 30 wherein thesecond series transition metal is selected from the group consisting ofzirconium and silver.
 35. The material of claim 30 wherein the group IIImetal is aluminum.
 36. The material of claim 30 wherein the group IVmetal is selected from the group consisting of tin (II), tin (IV), andlead.
 37. The material of claim 30 wherein the group II B metal isselected from the group consisting of zinc and cadmium.
 38. A fibrousasbestos material consisting essentially of asbestos fibers havingdeposited thereon hemolysis reducing tin (IV) molybdate.
 39. A fibrousasbestos material consisting essentially of asbestos fibers havingdeposited thereon a hemolysis reducing tin (II) molybdate.
 40. A methodof treating asbestos to reduce its hemolytic activity comprisingdepositing on at least a portion of the asbestos an effective amount ofa material consisting essentially of at least one metal molybdateselected from the group consisting of tin (II) molybdate, tin (IV)molybdate, iron (II) molybdate, and silver molybdate, to reduce thehemolytic activity of the asbestos to at least about 15 percenthemolysis.
 41. A fibrous asbestos material consisting essentially ofasbestos fibers having deposited thereon at least one metal molybdateselected from the group consisting of tin (II) molybdate, tin (IV)molybdate, iron (II) molybdate, and silver molybdate, said fibrousasbestos material being further characterized as having its hemolyticactivity reduced by said deposited metal molybdate to at least about 15percent hemolysis.